It was 10:30 a.m. on Nov. 7 when the two men showed up.
Donna Huanca was alone, getting ready to open Houston's Art Car Museum. "They looked like robots," she says.
She told the men, dressed in dark suits and carrying leather portfolios, that they would have to wait until the doors opened at 11. That was when they flipped out their badges: They were federal agents investigating reports of "anti-American activity" at the tiny art gallery.
To FBI special agent Terrence Donahue and Steven Smith of the Secret Service, it was a routine mission to check out one of the more than 435,000 tips they have received since Sept. 11.
To Ms. Huanca, whose gallery was opening "Secret Wars," an exhibit on US covert operations and government secrets, it was something else. "What's anti-American about freedom of speech?" the docent blurted out.
The incident, which ended after an hour of questioning, represents more than just a disturbing day for one museum staffer. Across the US, growing numbers of Americans are facing similar interrogations - apparently, they say, because they have criticized the government, President Bush, or the war on terrorism.
Not everyone is bothered by the inquiries. Indeed, by responding to a torrent of tips federal agents are doing exactly what many Americans want them to do.
But as the nation mounts a zealous campaign against domestic terror, some observers say federal agencies are walking a delicate line between checking out leads and trampling on free speech.
"If the FBI is investigating art exhibits at museums, then the line has been crossed," says First Amendment scholar David Cole at Georgetown University in Washington. "The FBI should investigate any credible leads where federal criminal activity may be undertaken. But it should avoid investigating any political conduct."
The rise in doorstep inquiries reflects, in part, a new law-enforcement reality. Suddenly, it may seem hard to know who might be the next to steer a plane into a building. It also reflects raw math. There are simply many more tips to check.